Dental impression materials are used to record the oral situation of a patient. The resulting hardened impression material captures the negative of the oral situation.
Most dental impression materials are typically delivered in a two or more paste form, containing a base paste and a catalyst paste, which are mixed prior to their application. The mixed pastes are typically applied with the help of a dental tray and/or a syringe-type device. Usually the hardened material can be removed after about one to about six minutes after application. The hardened impression material is used either for making a provisional restoration using a temporary crown and bridge material or for producing a positive model of the oral situation by casting the mould with e.g. gypsum. The obtained positive model is used for making the final restoration in the dental laboratory.
Different types of chemistry can be employed to formulate impression materials. Often used are polyether impression materials which cure by a cationic ring-opening polymerization of aziridines (e.g. Impregum™, 3M ESPE). Aziridine moieties containing components are typically cured by using acids.
Strong acids which can be used include substances like sulfonium salts, especially alkyl sulfonium salts or sulfonium salts derived from glutaconic acid. Those and others are described e.g. in US 2008/0200585 A1 (Klettke et al.), U.S. Pat. No. 4,167,618 (Schmitt et al.) and US 2003/0153726 A1 (Eckhardt et al.).
These materials are acknowledged for their beneficial curing properties which include a comparatively long working time and a so-called “snap-set” curing behaviour. This means, that the viscosity of these materials in the mixed state does not change significantly until the end of the working time and when the working time is over, a rapid curing takes place.
Especially when a long working time is desired, there may be the need to further accelerate the speed of the curing reaction to reduce the time during which a patient is treated with the impression material.
A long working time can e.g. be achieved by using imidazolium compounds as described in EP 0 110 429 A2 (Jochum et al.). The use of these compounds normally does not only increase the working time of the impression material but also increases the curing time in the mouth for the patients and often the curing time is more affected than the working time, unfortunately.
To accelerate the curing of these kinds of materials, the use of sulfonamide compounds is suggested in US 2006/0247327 (Klettke et al.). This document refers to a dental composition comprising ethylene imine compounds and a non-reactive compound containing a SO2—NH group. It is stated that by adding this non-reactive compound the speed of set of the composition to be hardened can be accelerated. Typically, the working time is also reduced. Adding sulphonamide groups containing compounds is, however, hot always possible or desirable.
US 2004/0149164 (Eckhardt et al.) relates to a mixture of elongated N-alkylaziridine prepolymers which can be used as a dental material. The mixture can contain various modifiers like finely divided fillers, pigments, thixotropic agents and surface-active substances.
U.S. Pat. No. 6,599,960 (Eckhardt et al.) relates to storage-stable cationically polymerizable preparations with improved hardening characteristics. The preparations can contain 0.0005 to 50 wt.-% of soluble and/or fine-particle organic and/or inorganic alkaline earth and/or alkali metal compounds. The preparation can be used for making dental impressions.
US 2003/0153726 (Eckhardt et al.) relates to a catalyst component containing a Broensted acid, water and at least one antacid-acting compound.
US 2009/0068619 (Klettke et al.) describes a dental composition comprising a prepolymer and a crosslinker having a molecular structure being different from the molecular structure of the prepolymer. The composition can also comprise a filler selected from non-reinforcing fillers and reinforcing fillers.
US 2009/0047620 (Klettke et al.) relates to self-disinfecting plastics, in particular to polyether or silicone based dental plastics and impression materials. The composition can also comprise a filler selected from non-reinforcing fillers and reinforcing fillers.